1. Field of the Invention
This invention relates to implantable medical devices, and more specifically, relates to chronically implantable devices for determination of a plurality of hemodynamic variables including but not limited to right atrial pressure and pulmonary arterial pressure.
2. Description of the Prior Art
Intravascular pressure sensors are known in the art. U.S. Pat. No. 4,407,296 issued to Anderson teaches a chronically implantable pressure transducer suitable for use in the cardiovascular system. A pressure transducer with an improved electronic circuit is taught in U.S. Pat. No. 4,432,372, issued to Monroe. A further improved pressure transducer is taught in U.S. Pat. No. 4,485,813, issued to Anderson et al. These pressure sensors have been directed to the control of artificial cardiac pacers using algorithms which convert measurements of pressure or change of pressure into pacing rate.
Increases in the complexity of pacemakers and other implantable medical devices have increased efforts at producing sensors and transducers to monitor a variety of physiologic functions. Such transducers allow the exploitation of the additional capability of such medical devices.
The measurements of pressures (particularly pulmonary wedge pressure and central venous pressure) inside the heart are typically used to determine the health of the patient and provide a proper therapy. A number of restrictions are placed on defining the approach to a chronically implantable pressure sensor. Three of these restrictions are:
(1) it is generally unacceptable to implant any hardware on the left side of the heart, so pressures are normally measured from the right side,
(2) a chronic wedge pressure measurement is unacceptable due to pulmonary infarction, and
(3) chronically implanted leads in the pulmonary artery have not yet been proven to be safe.
One system for treating a malfunctioning heart based on hemodynamics i.e., the pressure at a site in a patient's circulatory system is taught in U.S. Pat. No. 4,986,270 issued to Cohen.
None of these references teaches the use of a single chronically implanted absolute pressure sensor in the right ventricle for determining a plurality of hemodynamic variables, i.e., right atrial pressure, right ventricular pressure, and pulmonary arterial pressure in a patient.